The EPA says burning wood to generate power is ‘carbon-neutral.’ Is that true?

Author

Professor Emeritus of International Environmental Policy, Tufts University

Disclosure statement

William Moomaw receives funding from Rockefeller Brothers Fund. He is affiliated with Woods Hole Research Center (Board Chair), The Climate Group (Board Chair North America), The Nature Conservancy. (Board member Massachusetts chapter)

Environmental Protection Agency Administrator Scott Pruitt recently told a group of forestry executives and students that from now on the U.S. government would consider burning wood to generate electricity, commonly known as forest or woody biomass, to be “carbon neutral.”

The executives, who had gathered at an Earth Day celebration in Georgia, greeted the news with enthusiasm. But I did not.

Turning forests into fuel

Energy can be renewable. Or sustainable. Or carbon neutral. Or some combination. These terms are often used interchangeably, but they mean quite different things. Wind power and solar energy clearly have all three attributes. What about bioenergy – the heat released from burning wood and other plants?

Trees can eventually grow to replace those that were felled to produce wood pellets that are burned to produce electricity. That makes biomass very slowly renewable, if the replacement trees actually do grow enough to absorb all the carbon dioxide previously discharged.

Carbon accounting

To settle this debate, many of my colleagues and I believe it is essential to accurately account for all the emissions from burning wood for electric power. This is more than an academic exercise as biomass already produces significant emissions and industry observers foresee a nearly seven-fold increase in its use by 2050 from 2013 levels.

Also, experts see the carbon neutrality of forest biomass differently depending on the time frames they consider, and on their assumptions regarding the likelihood that saplings planted to replace burned trees grow sufficiently to offset all of the associated carbon emissions.

The UK’s Drax power station is among the largest to shift from coal to wood.

Some bioenergy advocates claim that the carbon dioxide emitted when utilities and industry burn wood for energy is removed instantaneously by other growing trees located elsewhere. As long as forests globally are removing more carbon dioxide than is being released from harvesting and burning them, they assert that bioenergy is carbon neutral until combustion emissions exceed the removal rate by live trees.

However, there do not appear to be any quantitative studies to support this concept.

People are adding nearly twice as much carbon dioxide as natural systems can remove every year. If forests and soils were not continuously doing their job of removing carbon dioxide from the atmosphere, concentrations would grow annually by 75 percent more than they do.

Like most bioenergy critics, I point out that this debate hinges on the choice of baselines for how and when one measures the net carbon impact of biomass emissions. Put another way, you can’t count trees – and the carbon they would remove – before they grow.

And if the utilities now using biomass were to deploy solar energy instead, more carbon would remain stored in forests and less would be released into the atmosphere.

But waiting for full-replacement forest growth is a best-case scenario. The forestry industry usually harvests trees for timber, pulp and other products before they grow to their full potential. And there is no assurance that saplings planted to replace trees cut for biomass will grow enough to meet carbon removal goals before being lost to fire, pests, drought or wind – or that the land where they are planted won’t be converted to agriculture, housing, office parks or parking lots.

Even using forest residues from harvesting, and thinnings from forest management aren’t carbon-neutral. Only expanding forests and lengthening times between harvests reduce emissions.

The author and tree expert Robert Leverett walking among 150-year-old trees in Connecticut’s McLean Wildlife Refuge.Connor Hogan, CC BY

Besides, the consequences of a changed climate, such as flooded coastal cities, irreversibly melted glaciers and sea ice, species extinction and more severe weather events like hurricanes is what really matters – not net carbon emissions. Eventual carbon neutrality does not assure climate neutrality. And even if tree regrowth were to counteract the carbon released through biomass, it would take decades. But the world needs to stall emissions growth now.

The evidence demonstrates that burning biomass worsens climate change. By contrast, protecting and restoring forests increases the removal and long-term storage of carbon from the atmosphere, a highly effective means for slowing global warming.